The invention relates to a valve drive device for an internal combustion engine, to an internal combustion engine with an engine brake, and to a method for operating the valve drive device.
A valve drive device for an internal combustion engine is already known from DE 10 2007 048 915 A1. The valve drive device comprises an axially displaceable cam element and an adjusting device. The adjusting device comprises a first engagement element that is provided for the purpose of displacing the cam element axially into a first switching position. Furthermore, the adjusting device comprises a second engagement element that is provided for the purpose of displacing the cam element axially into a second switching position. The adjusting device has a first slotted guide track in which the first engagement element is guided in the first switching position. Moreover, the adjusting device has a second slotted guide track in which the second engagement element is guided in the second switching position. The first engagement element is embodied so as to be positively coupled with the second engagement element.
It is particularly the object of the invention to provide especially reliable operation of an internal combustion engine.
The invention starts from a valve drive device for an internal combustion engine with an axially displaceable cam element and with an adjusting device comprising a first engagement element that is provided for the purpose of displacing the cam element axially into a first switching position and comprising a second engagement element that is provided for the purpose of displacing the cam element axially into a second switching position, with the adjusting device having a first slotted guide track in which the first engagement element is guided in the first switching position and a second slotted guide track in which the second engagement element is guided in the second switching position, and with the first engagement element being embodied so as to be positively coupled with the second engagement element.
It is proposed that the adjusting device comprise a triggering device that is provided for the purpose of detaining the first engagement element in the second switching position against a restoring force. Especially reliable engine operation, particularly including in the event of the failure of the triggering device, can thus be achieved. Additional triggering devices can be advantageously avoided. Furthermore, especially reliable frequent switching position changes can be performed, which is especially advantageous for an engine brake of a braking force machine, particularly of a heavy goods vehicle. The valve drive device is preferably provided for an internal combustion engine of a heavy goods vehicle.
The cam element is preferably supported so as to be rotatable and axially displaceable. A “rotatably and displaceably supported cam element” is to be understood in particular as being a cam element that is mounted in such a way as to be rotatable and axially displaceable in relation to a cylinder head or another stationarily arranged component of the internal combustion engine. Preferably, a support member receives the cam element in a rotatable manner and can be displaced axially, particularly together with the cam element, and is supported in an axially displaceable manner in the cylinder head. The term “axial” refers in particular to a main axis of rotation of the cam element, so the expression “axial” designates particularly a direction that extends parallel or coaxial to the main axis of rotation. Furthermore, the term “radial” refers in particular to the main axis of rotation of the cam element, so the expression “radial” designates particularly a direction that extends perpendicular to the main axis of rotation.
The cam element can be preferably displaced axially in order to change the valve lift. “Valve lift changeover” is intended particularly to refer to discrete switching between at least two valve actuation curves that define the actuation of at least one charge-cycle valve. A “cam element” is intended particularly to refer to an element that has at least one cam for actuating a charge-cycle valve. Preferably, only the first engagement element is provided for the axial displacement of the cam element in two opposite directions. In this context, a “first switching position” is to be understood particularly as an operating position. In this context, a “second switching position” is to be understood particularly as a trigger position and/or an engine-braking position. The restoring force is preferably at least substantially constant. The term “provided” is to be understood particularly as meaning specially embodied, laid out, equipped or arranged.
In another embodiment of the invention, it is proposed that the triggering device comprise an electromagnet that is provided for the purpose of detaining the first engagement element in the second switching position against the restoring force. Advantageously, the triggering device is provided for the purpose of providing a release force that extends radially starting from the cam element. In this way, an especially lasting and quick activation and/or maintaining of the second switching position can be achieved. This is especially advantageous if the valve drive device is used for an engine braking process.
Moreover, it is proposed that the triggering device comprise a return spring that is provided in order to exert the restoring force on the first engagement element in the direction of the first slotted guide track. Preferably, the return spring forms a helical compression spring. It is also advantageous for the restoring force to be aligned radially in the direction of the cam element. In this way, the first switching position can be advantageously activated and/or maintained without an external energy input. If the electromagnet fails, the first switching position can be reliably assumed.
Moreover, it is proposed that the return spring be provided for the purpose of guiding the first engagement element, after the electromagnet is switched off, into the first slotted guide track in order to perform a switching operation into the first switching position. In the event of an electrical malfunction of the electromagnet, operation can thus be advantageously continued in the first switching position. Advantageously, no external energy, such as electrical energy, is required to perform the switching operation into the first switching position.
Furthermore, it is proposed that the first slotted guide track be provided for the purpose of moving the first engagement element in an oscillating manner in a radial direction of the cam element when the cam element rotates in the first switching position. Preferably, the first slotted guide track has different distances to the main axis of rotation of the cam element when seen over a peripheral profile. The first engagement element can be advantageously advanced as a function of an angle of rotation of the cam element. Increased operational reliability can be advantageously achieved in this way.
In addition, it is proposed that the first engagement element be arranged in such a way in relation to the triggering device that the restoring force in a portion of the range of motion of the first engagement element than a release force of the triggering device acting on the first engagement element. “Release force” is to be understood in this context particularly as referring to a holding force and/or a magnetic force, particularly an attracting magnetic force. “Portion of the range of motion” is to be understood in this context particularly as referring to a part of a maximum possible displacement range. The triggering device preferably acts on the first engagement element only in a close range with a greater release force than the restoring force. A switching operation in an unwanted angle-of-rotation position of the cam element can thus be advantageously prevented. Advantageously, the triggering device can also be time-controlled in an imprecise manner and/or independently of an angle-of-rotation position of the cam element.
Moreover, it is proposed that the adjusting device comprise a lever element that supports the first engagement element and the second engagement element about a common swivel axis. Preferably, the swivel axis runs parallel to the main axis of rotation of the cam element. As a result, in a simple structural embodiment, a movement of the second engagement element can be coupled with the first engagement element. Additional triggering devices can be advantageously avoided. Synchronization between a movement of the first engagement element and a movement of the second engagement element can be achieved in an especially operationally reliable and durable manner.
Furthermore, it is proposed that the valve drive device comprise a camshaft for supporting the cam element in a rotationally fixed manner, with the adjusting device being arranged on a free longitudinal end of the camshaft. The valve drive device can thus be integrated with particular ease into an internal combustion engine. In this context, “free longitudinal end” is intended to refer particularly to a free end with respect to the main axis of extension of an element.
Moreover, an internal combustion engine with an engine brake having a valve drive device according to the invention is proposed. Here, the cam element can be switched with especially high frequency in order to reliably activate an engine brake.
Furthermore, a method for axially displacing a rotating cam element in two opposite directions from a first switching position into a second switching position with an adjusting device is proposed, with a first engagement element being positively coupled with a second engagement element, and with the first engagement element being detained by a triggering device in the second switching position against a restoring force. An especially high level of operational reliability can be achieved in this manner.
Additional advantages follow from the following description of the figures. FIGS. 1 to 9 show an exemplary embodiment of the invention. The drawings, the description of the figures and the claims contain numerous features in combination. A person skilled in the art will also view the features individually as proves expedient and group them together into other sensible combinations.